FORMATION AND CHARACTERIZATION OF A NEW MONOCLINIC LITHIUM MANGANESE OXIDE - M-TYPE LIXMNO2

A new lithium manganese oxide with formula LixMnO2 (x = 0.2-0.3), deno ted as m-phase, has been identified and isolated. First noticed as an intermediate phase during the early steps of the solid-state synthesis of Li-Mn-O spinels at low temperature, it can be isolated by extended annealing and grinding mixtures of finely divided beta-MnO2, and LiOH or Li2CO3 at 150 degrees C. Its X-ray pattern can be indexed as primi tive monoclinic with a = 938, b = 565.5, c = 490.6 pm and beta = 102.2 degrees. Thermogravimetric and X-ray investigations show that it is s table up to ca. 550 degrees C. The m-phase structure appears to be rat her rigid. It allows only limited lithium extraction in acidic medium and limited electrochemical lithium intercalation, with maximum revers ible capacity Delta x = 0.25 Li per formula unit. These properties con firm that it is a new oxide, with a rather different behaviour from th at of known spinel-type or layered Li-Mn-O compounds.